I bought a Lowrance 330 C last year at Cabellas and feel it is the best value for the dollars spent. Has external Satalite unit and is both sonar and GPS. I looked at the Navionics chips and found they were $200 for each section I fish and would have easily had to buy at least 2 charts at $200 each. Instead bought the Lowrance $100 chart. Put it in the machine and it blew up... Checked the rev of my software, 1.0.0 and called Lowrance. There is an upgrade. They sent to me on a chip...Great Support.. with instructions and it worked perfectly. Now have East Coast, West Coast and all the countours and real time bouy info via satellite. My choice is Lowrance.